The present invention relates to surge arresters for communication circuits, such as telephone lines and the like.
The type of surge arrester with which the present invention is concerned is one that is intended primarily for protection of wire conductors and equipment connected thereto from electrical overvoltage conditions which may result from lightning, electrical power faults, and the like. Surge arresters for this purpose take various forms. Frequently, they are of the type that contain an arc gap across which the overvoltage will be applied causing conduction across the arc gap to ground. After the overvoltage condition has passed, the protector returns to its normal or non-conducting state. The arc gap may comprise spaced carbon electrodes separated by air, or the arc gap may be in a sealed gas-filled tube. The sealed gas tube arrester is essentially a cold cathode discharge tube generally comprising a pair of spaced metallic electrodes sealed to the ends of a cylindrical insulator. Gas tube arresters have a much greater useful life than arresters embodying carbon electrode air gaps.
Since the overvoltage condition which may be applied to a surge arrester are not constant in magnitude, there is a demand for such durable arresters that will withstand many surges of varying magnitudes as well as large currents. Two desirable qualities of a gas tube arrester, in this regard, are long service life and reliability. It is known that enlarging the sizes of the arrester components will generally satisfy these requirements. However, in many if not most applications this approach is not desirable because of limited installation space and because of the prohibitive cost of such large surge arresters.
It is also known to provide discharge surfaces of the opposing electrodes of various configurations such as grid surfaces or concaves. However, electrodes of such design still tend to discharge primarily between the opposing flat electrode surfaces and the electrodes tend to disperse metallic particles towards the surrounding insulator walls due to ion bombardment during discharge. A buildup of such metallic electrode material on the surrounding insulator walls tends to cause discharge to take place between electrode and wall as well as between opposed electrodes, and to decrease the effective insulation between the electrodes. Thus, such surge arrestors tend to become defective and exhibit a deterioration in their rated spark-over voltages.